Current therapies delivered by means of self-administered injections include drugs for diabetes (both insulin and new GLP-A class drugs), migraine, hormone therapies, anticoagulants etc. Administering an injection is a process which presents a number of risks and challenges for user and healthcare professionals, both mental and physical.
Conventional injection devices typically fall under two categories—manual devices and auto-injectors. In a conventional manual device, a user must provide a force to drive a liquid medicament out of the device, e.g. by depressing a plunger. There are numerous disadvantages inherent with user of a manual device. For example, if the user stops depressing the plunger, less than a full dose of the liquid medicament may be delivered. Furthermore, the force required to depress the plunger may be problematic for elderly users or those with dexterity problems, which may lead to trembling or shaking when aligning or the injection and/or while administering the dose of the liquid medicament. In addition, the extension of the button or plunger of manual devices may be too great. Thus it can be inconvenient for the user to reach a fully extended button.
Auto-injectors aim to make self-administration of injected therapies easier for users. Auto-injectors are devices which completely or partially replace activities involved in medicament delivery of manual devices. These activities may include removal of a protective syringe cap, insertion of a needle into a patient's skin, injection of the medicament, removal of the needle, shield of the needle and preventing reuse of the device. This overcomes many of the disadvantages of manual devices. Injection forces/button extension, hand-shaking and the likelihood of delivering an incomplete dose are reduced. Triggering may be performed by numerous means, for example a trigger button or the action of the needle reaching its injection depth.
In some auto-injectors the energy to deliver the fluid is provided by a spring. However, in some auto-injectors the pushing force exerted by the spring for pushing the liquid medicament out of the syringe of the auto-injector may vary in an undesirable way throughout the delivery of a dose. This may lead to delivery of medicament at a non-constant force and thus may have a high impact on the user when the injection is triggered.